Device for the metered addition of fuel

ABSTRACT

The invention relates to a metering device for fuel, particularly diesel fuel, upstream of an oxidation catalyst of an exhaust gas system of an external combustion engine. According to the invention, downstream of a supply device for fuel, a closing valve and/or a metering valve and an injection valve are integrated in a fuel line. In the region of the metering device, at least one throttle restriction for damping pressure fluctuations is provided.

PRIOR ART

With a device for metering fuel, in particular diesel fuel, upstream of an oxidation catalytic converter, which device is known by the name Departronic, a fuel metering system for regenerating particle filters is offered particularly for heavy utility vehicles. The system makes it possible, with a purposeful injection of fuel, particularly diesel fuel, into the exhaust gas, to regenerate the particle filter by burning off the soot particles that have been deposited there. An expensive coating of the filter or an additional tank for an additive are not needed. The device for metering fuel, in particular diesel fuel, upstream of the oxidation catalytic converter is integrated with a low-pressure fuel circuit. It injects a precisely metered quantity of fuel into the exhaust system upstream of the oxidation catalytic converter, without compressed-air reinforcement. The exhaust gas temperature as it flows through the oxidation catalytic converter rises sharply in the exhaust system as a consequence. In the process, soot stored in the particle filter burns off. The flow rate is varied to suit actual requirements. The sturdy and completely maintenance-free system controls the fuel addition as needed and independently of the injection system of the engine.

DISCLOSURE OF THE INVENTION

According to the invention, a metering device for fuel, in particular diesel fuel, upstream of the oxidation catalytic converter of an exhaust system of internal combustion systems, is proposed, and a closing valve and/or a metering valve and an injection valve are integrated, downstream of a supply device for fuel, into a fuel line in which at least one device for damping pressure fluctuations is provided in the vicinity of the metering device. With the aid of the device for damping, the pressure peaks or pressure signals that occur in the metering device or in the exhaust system can be damped in such a way that no damage occurs to the individual assemblies or to the pressure sensors. This also means that pressure peaks are reduced so sharply that, while they are effective and are sensed at the individual sensors, nevertheless they no longer lead to damage to the pressure sensor. Thus on the one hand damage to the sensor components is precluded; on the other, it is ensured that an adequate pressure signal, which can be evaluated by the sensor system, is available.

It is advantageous that a metering unit for fuel, in particular for diesel fuel, which is connected to the device for damping pressure fluctuations is integrated with the metering device.

It is also advantageous that the device for damping pressure fluctuations is downstream of a low-pressure circuit or of a pump for fuel supply. In this way, the device for damping pressure fluctuations can readily be accommodated inexpensively in this system, for instance inside a metering unit of the metering device for fuel.

In a preferred embodiment of what the invention proposes, it is provided that the metering device and the metering unit are connected at least via a return line to a tank of the motor vehicle, and downstream of the connection point of the return line, the metering unit is connected to a fuel inlet having the device for damping pressure fluctuations.

It is also advantageous that the device for damping pressure fluctuations is provided in a housing part of the metering unit and has a container, or an expansion part, in the fuel inlet or in the fuel line, or in the housing part for receiving an additional fuel volume, and that the container or the expansion part for receiving an additional fuel volume is integrated into the metering unit between the closing valve and the metering valve. In this way, pressure fluctuations that occur can be damped and quickly detected, and then made available to the control device for continuous fuel supply. As a result, malfunctions or defects in the fuel line can be ascertained at that point, and depending on the magnitude of the problem, the fuel supply can be interrupted until such time as the problem in the fuel line is eliminated. Moreover, the container or the expansion part for receiving a fuel volume can advantageously be part of a valve block or of the fuel inlet or of the fuel line and can be formed for example by a widening of the tube.

It is also advantageous that at the fuel inlet or at the fuel line, the metering valve is provided with at least one pressure sensor downstream of the closing valve. As a result, it is advantageously possible to diagnose a torn-off line or a leak in the line. Optionally, the metering can be controlled even in the absence of the pressure sensor.

It is moreover advantageous that between the closing valve and the metering valve, at least one damping throttle restriction having a pressure sensor is connected to the fuel inlet. The at least one throttle restriction reduces pressure peaks upstream of the sensor and thus lessens the danger of damage to the sensor. From the pressure upstream of the metering valve and the required fuel quantity, the opening time of the metering valve can advantageously be calculated; optionally, there is the possibility of using a temperature sensor, in order to make a temperature-dependent correction of the quantity.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described below in further detail in conjunction with the drawings.

Shown are:

FIG. 1, a block circuit diagram of an example of a metering device, with various electromagnetically or electronically or pressure-controlled valves of the prior art;

FIG. 2, a first exemplary embodiment, in which a pressure sensor is preceded by a variable or static throttle restriction;

FIG. 3, a block circuit diagram of a further exemplary embodiment, with the possibility of integrating an additional damping member inside the pressure sensor connection.

EMBODIMENTS

It can be seen from the view in FIG. 1 that the fuel supply to a metering device 10 is effected via a pickup point at a low-pressure circuit 3 of a fuel injection system, not further shown in FIG. 1, of an internal combustion system of the vehicle. Via a throttle restriction 1 provided in a fuel inlet 16, fuel flows to a metering unit 4, which in FIGS. 1-3 is represented by a rectangular outline and is accommodated in a housing part, not shown in detail in the drawing.

In regeneration pauses, a closing valve 5 provided downstream of the throttle restriction 1 interrupts the inflow of fuel, especially diesel fuel, to the metering unit 4. With the closing valve 5 closed, the entire fuel volume flows back into a tank 7, via an overflow valve 6, embodied for example as a check valve. The overflow valve 6 is provided in a return line 7.1, which is connected between the throttle restriction 1 and the metering unit 4 to the fuel inlet 16 and which discharges into the tank 7.

The low-pressure circuit 3 is subject to pressure fluctuations, which can lead to impairments in function or even failure of pressure sensors 8.1 and 14.1 that will be described below. For that reason, damping provisions are advantageous, which as described below can be implemented with the aid of devices 14, 15 for damping pressure fluctuations, or with a damping member or an expansion part or a receiving chamber for an additional volume.

The connection of the pressure sensor 14.1, which can optionally also include a temperature sensor, to the fuel inlet 16 is effected via a bore provided in the metering unit 4. As a result of the direct connection of the pressure sensor 14.1, supply pressure fluctuations downstream of the closing valve 5 can be measured. To avoid or minimize pressure peaks and cavitation phenomena upstream of the pressure sensor 14.1, the following provisions can be made:

a) Simply connecting the pressure sensor 14.1 via the throttle restriction 15, provided in the metering unit 4, in accordance with the embodiment in FIG. 2.

b) Forming a generously designed fuel volume with the aid of the compensation chamber or of an expansion part 14, in accordance with the embodiment in FIG. 3.

By these provisions, cavitation peaks and supply pressure peaks can be damped. The metering of the injection of fuel is done with the aid of a metering valve 8.

If the closing valve 5 is opened, fuel can flow onward to reach the metering valve 8. The pressure sensor 14.1 is connected to the connecting bore between the closing valve and the metering valve 8, for optimally determining the requisite fuel metering quantity.

The pressure sensor 14.1, disposed downstream of the closing valve 5, serves to calculate the required metering quantity of fuel. This quantity is made available via the metering valve 8 and is delivered to an injection valve 9. The injection valve 9 is a passive valve, which opens at a defined supply pressure and injects fuel, in particular diesel fuel, into the exhaust system.

When used at the metering device 10, the injection valve 9 is screwed into a cooling body, not shown in the drawing, which is supplied directly via the coolant system of the vehicle engine. The cooling of the injection valve 9 can also be made possible with the aid of fuel, not shown in the drawing, flowing past the injection valve 9.

In the exemplary embodiments shown in FIGS. 2 and 3, the metering device 10 for metering fuel, in particular diesel fuel, is disposed upstream of a particle filter and an oxidation catalytic converter, which are not shown for the sake of simplification.

The basic connection of the pressure sensor 8.1 is the same in FIGS. 2 and 3. In the variant embodiment of FIG. 2, the pressure sensor 14.1 is downstream of the closing valve 5 and is connected to the fuel inlet 16 via a throttle restriction 15. A connection can be implemented through a connecting bore for instance, if there is an eroded throttle restriction. In that case, the connection of the pressure sensor 14.1 is effected to the fuel inlet 16, by means of a sheath and a sealing ring.

In the embodiment of FIG. 3, downstream of the closing valve 5 or in the pressure sensor 14.1 or in the metering unit 4 or in the fuel inlet 16, an additional volume is made available with the aid of a volume container 14. The volume container 14 may be embodied as a widening in a bore, for instance. Furnishing an additional volume (>10 cm³ is recommended) serves as a damping volume inside the connection of the pressure sensor 14.1. For that purpose, an expanded or additional bore can be provided in the metering unit 4 as well. Taking strength requirements into account and/or by optimizing the weight, aluminum blocks of solid material present in the metering unit 4 can be drilled or milled out, in order to furnish the aforementioned flow connections or the additional volumes that serve the purpose of damping.

The metering device 10 in FIGS. 2 and 3 is connected to the low-pressure circuit 3. Via the fuel inlet 16, the closing valve 5, the metering valve 8, and a fuel line 2, the injection valve 9 is connected to the low-pressure circuit 3. With the aid of the fuel flowing by, cooling can be done inexpensively, since the exhaust gas temperature as it flows through the oxidation catalytic converter rises to approximately 600° C. Moreover, rapid aging of the fuel stored in the injection valve 9 can be avoided, with the aid of a cooling device not shown in the drawing. Shortly before the outlet opening of the injection valve 9, a fuel return line can be connected to the fuel line 2, and this return line leads back to the tank 7 via a controllable or regulatable pressure valve.

The switchable and/or controllable or regulatable closing valve 5 and/or the switchable and/or controllable or regulatable metering valve 8 can also be provided in the fuel inlet 16 or in the fuel line upstream of the injection valve 9. The metering valve 8 and/or the closing valve 5 are triggered in clocked fashion via a control device of the motor vehicle. 

1-9. (canceled)
 10. A metering device for fuel, in particular diesel fuel, upstream of an oxidation catalytic converter of an exhaust system of an internal combustion system in a motor vehicle, in which downstream of a supply device for fuel, a closing valve and/or a metering valve and an injection valve are integrated into a fuel line, and in the vicinity of the metering device, at least one device for damping pressure fluctuations is provided.
 11. The metering device as defined by claim 10, wherein a metering unit for fuel, in particular diesel fuel, is integrated with the metering device and is connected to the at least one device for damping pressure fluctuations.
 12. The metering device as defined by claim 10, wherein the at least one device for damping pressure fluctuations is downstream of a low-pressure circuit or a pump for fuel supply.
 13. The metering device as defined by claim 10, wherein the metering device or the metering unit is connected at least via a return line to a tank of the motor vehicle, and downstream of a connection point of the return line to a fuel inlet, the metering unit is provided with the at least one device for damping pressure fluctuations.
 14. The metering device as defined by claim 11, wherein the metering device or the metering unit is connected at least via a return line to a tank of the motor vehicle, and downstream of a connection point of the return line to a fuel inlet, the metering unit is provided with the at least one device for damping pressure fluctuations.
 15. The metering device as defined by claim 12, wherein the metering device or the metering unit is connected at least via a return line to a tank of the motor vehicle, and downstream of a connection point of the return line to a fuel inlet, the metering unit is provided with the at least one device for damping pressure fluctuations.
 16. The metering device as defined by claim 10, wherein the at least one device for damping pressure fluctuations is provided in a housing part of the metering unit and includes a container, or an expansion part, in a fuel inlet or in the fuel line, or in the housing part for receiving an additional fuel volume.
 17. The metering device as defined by claim 11, wherein the at least one device for damping pressure fluctuations is provided in a housing part of the metering unit and includes a container, or an expansion part, in a fuel inlet or in the fuel line, or in the housing part for receiving an additional fuel volume.
 18. The metering device as defined by claim 12, wherein the at least one device for damping pressure fluctuations is provided in a housing part of the metering unit and includes a container, or an expansion part, in a fuel inlet or in the fuel line, or in the housing part for receiving an additional fuel volume.
 19. The metering device as defined by claim 13, wherein the at least one device for damping pressure fluctuations is provided in a housing part of the metering unit and includes a container, or an expansion part, in the fuel inlet or in the fuel line, or in the housing part for receiving an additional fuel volume.
 20. The metering device as defined by claim 14, wherein the at least one device for damping pressure fluctuations is provided in a housing part of the metering unit and includes a container, or an expansion part, in the fuel inlet or in the fuel line, or in the housing part for receiving an additional fuel volume.
 21. The metering device as defined by claim 15, wherein the at least one device for damping pressure fluctuations is provided in a housing part of the metering unit and includes a container, or an expansion part, in the fuel inlet or in the fuel line, or in the housing part for receiving an additional fuel volume.
 22. The metering device as defined by claim 16, wherein the container or the expansion part for receiving an additional fuel volume is integrated into the metering unit between the closing valve and the metering valve.
 23. The metering device as defined by claim 21, wherein the container or the expansion part for receiving an additional fuel volume is integrated into the metering unit between the closing valve and the metering valve.
 24. The metering device as defined by claim 16, wherein the container or the expansion part for receiving an additional fuel volume is part of a valve block or of a fuel inlet or of the fuel line.
 25. The metering device as defined by claim 21, wherein the container or the expansion part for receiving an additional fuel volume is part of a valve block or of the fuel inlet or of the fuel line.
 26. The metering device as defined by claim 10, wherein downstream of the closing valve at a fuel inlet or at the fuel line, the metering valve is provided with at least one pressure sensor.
 27. The metering device as defined by claim 11, wherein downstream of the closing valve at a fuel inlet or at the fuel line, the metering valve is provided with at least one pressure sensor.
 28. The metering device as defined by claim 10, wherein between the closing valve and the metering valve, at least one damping throttle restriction having a pressure sensor is connected to the fuel inlet.
 29. The metering device as defined by claim 11, wherein between the closing valve and the metering valve, at least one damping throttle restriction having a pressure sensor is connected to the fuel inlet. 